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Table DR1. Radiocarbon ages for the eruption of Ulmener Maar (calibration by OxCal 4.1.; Bronk Ramsey 2009). *Arithmetic mean and standard deviation, not considering the bulk organic and humid acid based dates published by Büchel and Lorenz (1982). Sample ID Site Material Method Age (14 C yr BP) Age (cal. BP) Reference

Recent developments in optically stimulated luminescence (OSL) dating allow the determination of signals in increasingly smaller sample amounts. This has led to microdosimetry having a larger impact on equivalent dose (D E ) distributions and therefore, detection and assessment of spatial distribution of radionuclides has become more important. This study demonstrates the application of autoradiography using imaging plates to determine spatially resolved radiation inhomogeneities in different types of samples. Qualitative evaluations of radiation inhomogeneity are carried out on unconsolidated sediments as well as on hard rock samples. While indicating some limitations of applicability, the results demonstrate that the method is an efficient tool to detect and document spatial variations in a sample's radiation field. It therefore provides a possibility to rapidly screen samples to check whether microdosimetry might affect the D E data. Furthermore, an approach to calibrate autoradiographic images for quantitative use is suggested. Using pressed powder pellets of reference materials, a series of calibration images were exposed, from which a functional relation between specific sample activity and greyscale value in the autoradiographic image has been deduced. Testing the calibration on a set of 16 geological samples, of which their radionuclide content is known, shows a good correlation between specific activities calculated from the nuclide content and specific activities deduced from the autoradiographic images. These findings illustrate the potential of autoradiography with imaging plates to detect spatial distributions of radionuclides and to tackle certain aspects of the problem of microdosimetry in modern trapped charge dating.